Production of photographic and cinematographic color positives



Oct. 22, 1935. J. E. THORNTON 2,018,196

PRODUCTION OF PHOTOGRAPHIC AND CINEMATOGRAPHIC CLOR POSITIVES Filed May 10, 1934 gi/wl /myf hav/ny been dixo/friend removed.

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Patented Oct. 22, 1935 UNITED STA-Tas PRODUCTION or"v Pno'roGaAPmc AND cTNEMAToGnArmc coLoa rosrrrvns .lohn dward. Thornton, Jersey, Channel Islands Application May 10, 1934, -Sel'ial N0. 724,.:98 AIn Great Britain April 6, 1934 Claims. (Cl. 95-2) This invention relates to a method or process for producing photographic and cinematographic multi-color positive pictures of the subtractive type and comprising either two or four colors.

One feature of the invention is* that these subtractive positives are of full-tone character but are produced from camera-originals or negatives which have images of colored broken-tone character, such as mosaic, lenticular, prismatic, diffraction, line-screen, or the like.` In the following description the term mosaic is used for convenience, to include any or all of these different forms of broken-tone images, and their different varieties are hereinafter more fully described in detail.

Another feature is that the positives are made in various forms,l for example as photographic color prints mounted upon paper or other reilective opaque backing for viewing by reflected light; upon cellulose or transparent paper for lamp shades and other decorative or advertising transparencies; upon a temporary paper support for use as a transfer to any desired surface; upon glass or cellulose for use yas lantern slides for projection; upon cinematograph lm' for enlarged projection on to a screen; or in any other desired and suitable form for any purpose.

A. third feature is that these subtractive positives are of a type and character that are entirely free from light-obstructing silver deposits and will pass a very much greater percentage of light than the mosaic or other originals or any mosaic positive made therefrom by the old orthodox methods of mosaic reproduction.

A fourth feature is that the subtractive positives are made in two parts, as two part-pictures in two sensitized areas upon opposite sides of a thin transparent support', from a negative in which the color parts or color-separations are contained in only one picture area as intermixed colors.

Hitherto mosaic-color paper-prints have been so dull as to be practically valueless, because half the light which should be otherwise reflected back bythe white paper support has been yblocked out partly by a deposit of metallic silver in the image. But in subtractive paper prints prepared by this invention there is no silver in the image, and therefore 100% of the light is reflected back less the amount absorbed by the opaque support and yby the colored colloid forming the image., and

for that reason color prints made by this processare clear, transparent, and as brilliant as the regular type of monochrome print. l

subtractive transparencies from mosaic or ter. V

other broken tone negatives prepared byy this y invention upon thicker transparent supports, are

as transparent and brilliant as the-reflective pa-v per prints aforesaid, because the colored imagesv contain no silver.

subtractive positives made according to this invention are formed intwo parts in two layers of gelatino-silver panchromatic emulsion which is coated upon opposite sides of a transparent cellulose film, each layer being adhered to the support by the usual adhesive substratum. To prevent light projected upon one emulsion during printing from passing through to the other emulsion, a light-obstructing medium is coated between the two layers of emulsion, as in my l5 Patent No. 1,250,713, or alternatively the two emulsion layers may be stained with a, soluble dye that will answer the same purpose. Either kind of light-obstructing'medium is washed out 'during subsequent operations.

For mounting as a reilective print on paper or other reflective backing, the positive is made as an extremely thin leaf, almost like tissue, and its cellulose support may be as thin as In of an inch or less; also its coloring is very thin and delicate, in order that as much light as possible may pass through and be reected back from the opaque backing.

For a transparency -or a cinematograph lm a much thicker cellulose support may be used, such as im of an inch, or any other, thickness according vto requirements; also the-coloring is more intense than for a reflect-print and the general density of the image is greater for projection.

The invention is illustrated in the accompanying drawing in which it is shown applied to the production of a 2color subtractive positive picture the partial images of which are. formed on opposite sides of a transparent support. In this drawing:-

Fig. 1 is a section throughthe sensitive mate-'- rial yfor making the 2color subtractive positive of full-tone character from a 2color negative of broken-tone character.

Fig.-2 is a section through the sensitive material after development therein of a pair of black metallic silver images, and after the application to such images of an ozoplaster which comprises a porous paper support or backing on to which is coated liquid colloid having the desired coloring matter incorporated therewit Fig. 3 is a section through the finished 2color subtractive positive picture of full-tone characduring printing from passing through to the other emulsion, a light-obstructing medium is 'coated between the two layers, as described in my prior Patent No. 1,250,713, or valternatively the two emulsion layers may be stained with a soluble dye for the same purpose. In either case the light-obstructing medium is washed out during subsequent operations.

In producing the 2-color subtractive positive picture from a 2-color (or more than 2-color) camera-original or negative picture (which is color-screened or defined in colors which are complementary to those of the; original scene) the rst step is to formupon one ofthe emulsion layers B1 of double-sensitized lm a positive of metallic silver which represents one color-part of the mosaic negative say the red part, and also to form upon the opposite layer B2 'of the film another positive of metallic silver which represents the other color-part of the mosaic negative, say the green.

`This double-sided positive print from one 2- color negative is produced by placing the mosaic negative in an optical printing apparatus and projecting two images of the negative on to opposite sides of the positive film, both images being back-to-back, in exact registry one with the other. These two images both alike may be projected and formed by any known optical arrangement. During projection the fine dots or lines of the mosaic image are very slightly spread or enlarged, so that in the image upon the sensitive positive lm the dots will practically join up to produce the desired full-tone image. This spreading is effected by any ofthe various known methods used in spreading mosaic-image dots, for example a ground glass or a lenticular screen is placed between light and negative; or a prism double-image device or an optically plane angularly rotating disc may be interposed in the light beam between negative and positive films, or any other effective known means may be used.

'One of the images is projected through a red color-iilter C1 which allows only the red light topass, and therefore only the red-colored part of the mosaic negative is impressed upon that side of the sensitive lm.

The other image is projected through a green color-nlter C2 which allows onlyY green light to pass, and therefore only the green-colored part of the mosaic negative is impressed upon the opposite side of the sensitive film, back to back against the red-colored part.

The system of optical printing through color filters is somewhat slow, but this is not a serious objection in producing amateur or other photographs where usually only one or a few copies are required.

But when the invention is applied in the production of cinematograph film positives, where the editions required generally comprise many copies of enormous lineal footage and have to be printed quickly, it is convenient to speed up production very greatly by making only one fulltone subtractive copy from the mosaic original.- and then use this full-tone copy as` a printingclich from which positive copies can be printed very quickly by the more rapid -methods of subtractive color or monochrome printing. 'Ihe 5 before described. It is necessary that the clichimage should be made of negative character, this may be ensured in making ythe clich by utilizing either the known method of chemical re- 1;

' versal, or the known method of hardening, the

gelatine of the silver image and bleaching and dyeing the non-hardened gelatine.

The exposed and printed film is then developed, thus producing a pair of component-positive images D1 and D2 of subtractive full-tone character and of metallic silver upon opposite sides of the lm (see Fig. 2) both of which represent the same tone gradations as those ofthe original negative.

The iilm may then be iixed, washed and dried. prior tothe next operation of coloring. 0r if desired such coloring operation may proceed upon the still wet images after development and washing and before fixing. v 3o The next operation is that of bleaching and coloring the s'ubtractive images of metallic silver.

'I'his operation consists inapplying and rmly adhering'and uniting to each surface of the gelatin-silver image-layer' a. layer of colored colas loid, a different colorupon each side for each component image, which may be applied by any known means and method.

'I'he preferred method consists in applying what I term an ozoplasterf El, E2 to each of the me- 40 tallic silver images. Such ozoplaster consists of a porous paper support or backing on to which is coated liquid colloid in which the desired coloring matter is incorporated, and which may be a substantially waterf-insolubleorganic dyestufl' in 45 a colloidal state of subdivision, or a transparent pigment or mordanted dye, or insoluble dyelake) or other suitable coloring agent. as now used in the preparation of what is commonly known as carbon tissue. As shown'in Fig. 2a green oao- 50 plaster E1 is applied to the image D1 printed through the red :filter B1 and a red ozoplaster E2 is applied to the image. D2 printed through the green filter B2. Instead of using an Y colloid, may be applied to the image of metallic silver in liquid form, by any of the known methods of coating, brushing, floating, or the like, and is then set or dried.

Various forms of colloid may be used, either s0 alone or mixed, such as gelatine, glue, sh-glue, albumen, gum-arabic, gum tragacanth, agar, or casein. 'I'he solvent used for developing the colloid image into relief is therefore chosen according to the colloid selected. For gelatine and glue it will be warm water, and for other colloids cold water or other suitable solvent. After application of the colored colloid the silve images D1 and D2 are next .treated in a bleachhardening solution of well-known type, which 70 usually contain soluble bichromate, .ferricyanida and bromide salts, or in other cases copper salts. or in others chromic acid. Any suitable known formula may be used. IIhe effect of treatment in such a bath is that the silver is bleached and 15 o'zoplaster the colored sa the colored colloid in contact with the silver is rendered insoluble in exact proportion to the amount of silver in the image, `and the colored colloid becomes rmly united tothe gelatine of the silver image by a process of physical interlocking of the two layers.

The bleached and colored images are then as the common hypo bath or ferricyanide andv hypo. 'Ihis renders the image clear and transparent.

The order of application of the silver solvent and the colloid solvent may be exchanged. b Finally the images are lwashed and dried.

If the colored colloid is of a kind-soluble in Warm water, such as gelatine or glue, it is necessary that the gelatine layer containing the silver image should be insoluble in such solvent. It is therefore hardened at some suitable stage of manufacture, with chrome alum, formaldehyde, vor otherl hardening agent, and this may be effected during manufacture -of the sensitive film or during processing treatment before applyingl warm water solvent. Or a hardener may be incorporated in the fixing bath, warm water treatment being used later.

If the colored colloid is of a kind soluble in cold water such as gum-arabic for example, no hardening of the gelatino-silver layer is necessary. 'i

In the foregoing specification red and green have been used as a simple illustration. But in most 2-color pictures it is-preferred to use orangered and blue-green as the complementary pair of colors to produce the most pleasing result. 'I'he invention is not restricted to any particular combination of coloring. In some cases blue-violet and orange might be used.

As will be seen from the foregoing description a feature of the invention is that the complementary or inverted colors of the broken tone negative are corrected in the subtractive full tonel positive by applying each ozoplaster or layer of colored colloid to the opposite side of the negative than the color-record as first formed, and by this means what would otherwise prove wrong coloring in the positive (as compared with the original scene owing 'to having to print through a positive color-filter of the same color as the inverted color of the negative) is thus corrected and Vmade to rightly correspond to the color of the original scene.

'I'he picture resulting from the process described will comprise in its first stage two subtractive images of metallic silver D1 and D2 embedded in two lower layers of gelatine B and B2 as shown in Fig. 2 whilst in its final stage (which is shown Lin Fig. 3) it comprises two subtractive relief images F1 and F2 of insoluble colored colloid in upper layers f1 and f2 superimposed upon the lower layers B1 and B2 of gelatine from which the original subtractive images of silver have been removed. By this means are formed a subtractive picture with `a very high degree of transparency and luminosity, which is free from the light-obstructing agents of the old type of mosaic positive, such as the mosaic colorfilter screen and the filter-blocking mask of black-silver.

The completepositive therefore consists of two partialor component positives of transparent colored colloid alone, in full tone formation, each supported upon a layer of transparent-gelatine from which all silver has been removed. Such positive can be utilized in a number of different ways and for dierent purposes.

1 The invention canbe extended to produce 4- color pictures in the same manner by using'apair of mosaic negatives which record four color-separations asdescribedin myPatent No. 1,700,618. The 4-color positive is made by exactly the same procedure as the 2-color hereinbefore described, but the positive film is of doubled area, so that it presents four sensitive picture-areas to the-four projected 4negative images, and four color-filters are used to separate the four colors, so that only one component of the four is printed upon each 20 sensitive surface. The two positive films are then developed as before,l and four ozoplasters or'four layers of colored colloid are applied, followed by 'bleach-hardening, relief development, and silver removal as before.` After washing and drying the two films are superimposed and cemented together in accurate image registry one with the other,'and thus form a complete subtractive fulll tone picture of four colors.

The colors for a 4-color picture are preferably. formed as two complementary pairs, for example, crimson-violet and green, blue-violet and' orange; or red, green, blue', yellow, or any other desired combination.

To simplify the procedure only one film material for the positive and two ozoplasters may be used (as in the 2color example) by making the positive film-material of double area and the ozoplasters of double area with their differentlycolored areas adjacent to each other.

Also the process canbe used as partof a 3- color picture; the third color, which may be yellow, is formed upon another support such as paper, and the two-color portion is cemented over it, in which case the two colors of the subtractive full-tone positive from the mosaic negative would be red and blue and the cemented positive yellow. But other combinations of colors may be substituted s uch as blue-green and red.

The mosaic negatives or printing clichs colors of the original scene or object photographed. 'Ihe best of these for use with this invention are those known as mosaic negatives.

In its common form this type of negative is generally made with a mosaic lter which gives an analysis of three colors in one picture area, and consists of 'a transparent support upon which is superimposed a mosaic screen of microscopically small colorlters laid side by side in the same plane and intermingled in close juxtaposition. On this mosaic color-filteris coated a layer of panchromatic sensitive gelatine-silver emulsion of high speed, which is exposed in the camera through the mosaic-filter, then developed, and thus is produced a black mask of silver which `def-Ines the image' and gradations and blocks out parts ofl the mosaic filter. The uncovered parts represent the mosaic colored negative, and if the developed image is fixed only, and is not treated by the usual chemical-reversal process (for turning into a positive) its colors are compleinentaryv to those of the scene or object photographed.

The preferred form of mosaic-negative 'for 5 making 2-col0r full-tone subtractive positives by this invention comprises only two colors.

And instead of these two being the strong deepv colors which are necessary when the negatives is v required to be changed into a positive, the lters are made of specially light and transparent colorings, sov that the camera-exposures can be much shorter or more rapid. And, because Aof the lighter filter-colors. shorter exposures' are 'required in printing from such negatives. vThe same rule can be followed in making mosaic negatives for producing 4-color mosaic positives.

By departing from orthodox filter-coloring in the mosaic negative lters in the ,manner described, very great technical advantages accrue in the processesy of reproduction therefrom.

As the, mosaic negatives for use in this invention are only fixed, and are not subsequently treated by the usual chemical reversal process,

the colors shown in these direct negatives are complementary tol the original colors of the scene or object photographed, and it is therefore necessary to correct them byv acolor-reversal and not a negative-reversal method. In the present invention this is accomplished by applying to each side of the printed positive of silver images an ozoplaster of a color whichis the same as that of the original scene or object and is complementary to the color seen in the negative, as hereinbefore described.

For producing 2-color positives any other standard form of mosaic negative may be used, such as the ordinary 3-color mosaic which makes three separate color-analysis, or even a mosaic negative which makes four color-analysisin the same picture-area of the same negative may be used for producing the 2-color positives.

If the 2-color full-tone subtractive positive made according to this invention is reproduced from such a 3-coloror 4-color (mosaic or other color-illtered broken-tone) original negative, then the color scale of the positive represented in only two parts or color-.separations will be somewhat wider in each part of the positive than in each part of the negative, because each part of the positive, will reproduce portions of two por-` tions of. each negative, whether such negative be of 3-color or 4-color form. This method of making a 2-color full-tone subtractive positive from a negative which represents more than two colorseparations therefore has considerable technical advantages. In a further extension of the invention 4-color full-tone subtractive positives are made with four separate color-separations upon four sensitive areas. In one preferred method of doing this a set of 4-color mosaic negatives is used which are made according to Patent 1,700,618, in which the four colors are represented in a doubletwb pair of negatives which combined comprise an analysis of four colors.

By'applying the aforesaid system of increasing the color scale the 4,-color full-tone subtractive positives are made with four separate color-separations of a wider range by using a double-three pair of negatives containing an analysis of six colors, which are condensed into four positive images of wider color range.

Modified or alternative forms of-negatives 75, Another form of broken-tonev negative clich is that'known as a lenticular negative. To make subtractive full-tone positives from such lenticular negative it is projected through the same or a similar lens and multi-color lter used in taking the negative, on to the double-sensitized posi- 5 tive lm, after which procedure is as herein- Y. before described.

Other types of broken-tone clich or negativesystems of color-separation which can be used for projection as colored negative images for making full-tone subtractive color positives according to'this invention in conjunction with suitable optical apparatusand color filters, are` those known under such various names and types `or classes as prismatic, prismatic-dipersion, 1

diffraction, wedge-screen. line-screen, and the like.

State of thev art It is already known to form mosaic dot images upon both sides of a positive film by printing completely through the 111m from a mosaic negative applied to one Vside of the nlm by alternately covering the negative with differently colored filters. l

In such cases the positive images have been colored by the application of dyes to each side separate, which is an unsatisfactory method, and- Y incapable of giving the perfect images attained by the present invention.

vSilver images formed by printing through are notsuitable for coloring by-applied layers of colored colloid because it could not come in contact with the bases of the silver images and because the colored colloid layer upon thel rear side of the support would partially 'dissolve in the 35 solvent and oat oi. I

vOnly by projection printing ofy the primary silver images vsimultaneously from the same negative upon opposite sides of the support with the bases of such silver image outward, is it possible to make colored colloid images with theirV bases inwards and points outward, and form bases of On cinematograph hlm positivesy it is necessary 45 to add a sound record. This is printed in the margin, as a metallic silver positive, and in the coloring process is treated so that it may remain black-silver, or be made practically colorless, or 50 may be changed to a colored record, according to the-methods described in my concurrent application Serial No. 718,440 filed March 31, 1934.

What I claim as my invention and desire to protect by Letters Patent is:

1. A process for producing, from a multi-color broken-tone picture, of negative character, a multi-color photographic or cinematbgraphic positive picture of highly transparent character, built up from two relief images of subtractive full- 60 tone type formed of insolubli'zed colored colloid containing no silver, and in superimposed back to back registry, the said process comprising the followingv operations or stepsz-(a) projecting two images both alikel of the one multi-color 55 broken-tone negative picture onto opposite sides of a double-sensitized positive illm in superimposed back-to-back registry, the light-rays of the complementary color which' cuts out all other colors but theone, and exposing and printing the other partial-positive image upon the other side of the film through a filter of the other complementary color which cuts out all other colors but the one; (c) developing and forming a pair of metallic silver images upon opposite sides of the film which are complementary to each other; (d) applying a layer of colored colloid to each of the silverimages, each layer of colloid being oi' a color which is the same as the original subject and is complementary to the color of the negative, and is complementary to the other layer of colored colloid; (e) treating the colloid-colored film in ableach-hardening bath to form images of insolubllzed colored colloid; (f) dissolving the surplus colored colloid in a solvent bath; (g) dissolving the silver salts in another solvent bath; (h) finally washing and drying the film; thereby producing a color-positive comprising a pair of colored-colloid relief images adhering to andsuperimposed upon a pair of silverless imageless transparent gelatine layers which are rmly adherent to opposite sides of the transparent support, and in colors which are'the same as the original object and complementary to the colors of the negative.

2. A process for producing, from a multi-color mosaic picture of negative character comprising inverted coloring, a multi-color photographic or cinematographic positive picture of highly transparent character, built up from two relief images of subtractive full-tone type formed of insolublized colored colloid containing no silver and in superimposed back to back registry, the said process comprising ythe following operations or stepsz-(a) projecting two images both alike of the one multi-color broken-tone negative picture on to opposite sides of a double-sensitized positive film in superimposed back-to-backregistry,4

the light-rays of the said negative images ol broken-tone character being slightly spread diverted or scattered in the process ol' projection to form images of full-tone character; (b) separating the colors by a pair of complementary filters during projection, by exposing and printing one partial-positive image upon one side of the film through a iilter of one complementary color which cuts out all other colors but the one, and exposing andv printing the other partial-positlve image upon the other side of the film through a filter of the other complementary color which cuts out all other colors but the one; (c) developing and forming a. pair of metallic silver images upon opposite sides of the film which are complementary to each other; (d), applying a layer of colored colloid to each of the silver images, each layer of colloid being of a color which is the same as the original subject and is complementary to the color of the negative, and is complementary to the other layer of colored colloid; e) treating the colloid-colored film in a bleach-hardening bath to form images of insolublized coloredcolloid; (f) dissolving the surplus colored colloid in a solvent bath; (g) dissolving the silver salts in another solvent bath; (h) finally washing and drying the film; thereby producing a color-positive comprising a pairA of coloredcolloid relief images adhering to and superimposed upon a pair of silverless imageless transparent gelatine layers which are firmly adherent to opposite sides of the transparent support, and in colors which are the same as the original object and complementary to the colors of the negative.

3. A process for producing, from a multi-color lenticular picture of negative character, a multicolor photographic or cinematographic positive picture of highly transparent4 character, built up from4 two relief images of subtractive full-tone type formed of insolublized colored colloid containing no silver, the said process comprising the following operations or steps:(a) projecting two images both alike of the one multi-color broken-tone negative picture on to l0v opposite sides of a double-sensitized positive film in superimposed back-to-back registry, the lightrays of the said negative images of broken-tone character being slightly spread diverted or 4scattered in the process of projection to form images i of full-tone character; (b) separating the colors by a pair of complementary filters during projection, by exposing and printing one partialpositive image upon one side of the iilm through a lter of one complementary color which cuts 20 out all other colorsbut the one, and exposing and printing the other partial-positive image upon the other side of the lm through a filter of the other complementary color which cuts out all other colors but the one; (c) developing 25 and forming a pair of metallic silver images upon opposite sides of the lm which are complementary to each other; (d) applying a layer of colored colloid to each of the silver images. each layer of colloid being of a color which is Il the same as the original subject and is complementary to the color of thel negative, and is complementary to the other layer of colored colloid; (e) treating the colloid-colored lm in a bleach-hardening bath to form images of in- 86 solublized colored colloid; (f) dissolving the surplus colored colloid in a solvent bath; (y) dissolving the silver salts in another solvent bath; (h) finally washing and drying the film: thereby producing a color-positive comprising a pair 4o of colored-colloid relief images adhering to and superimposed upon a pair of silverless imageless transparent gelatine layerswhich are firmly adherent to opposite sides ofthe transparent support, and in colors which are the same as the 45 original object and complementary to the colors of the negative.

4. A process for producing, from a multi-colory broken-tone picture of negative character. a multi-color photographic or cinematographic l0 positive picture of highly transparent character, built up from two relief images of subtractive full-tone type formed of insolublized colored colloid containing no silver, andin superimposed back to back registry, the said process compris- B5 ing the following operations or steps:-(a) projecting two images both alike ol' the one multicolor broken-tone negative picture on to oppo.; site sides of a double-sensitized positive lmjin superimposed back-to-back registry, the lightf rays of the said negative images oi' broken-tone character being slightly spread diverted or scattered in the process of projection to form images of full-tone character; (b) separating the colors by a pair of complementary filters during projection, by -exposing and printing one partialpositive image upon one side of the film through a lter of one complementary color which cuts out all. other colors but the one, and exposing and printing the other partial-positive image 70 upon the other side of the film through a lter of the other complementary color which cuts out all other colors but the one; (c) developing and forming a pair of metallic silver images upon opposite sides of thel iilm which-are comple-r mentary to each other;` (d) applying a plaster consisting of a. porous paper support or backing carrying a layer of colored colloid incorporating the desired coloring matter to each of the images of metallic silver; (e) treating the colloidcolored film in a bleach-hardening bath to form images of insolublized colored colloid; (f) dissolving the surplus colored colloid in a solvent bath; (g) dissolving the silver salts in another solvent bath; (h) finally washing and drying the film; .thereby producing a color-positive comprisingfa pair of colored-colloid relief images adhering to and superimposed upon a pair of silverless imageless transparent gelatine layers which are iirinly adherent to opposite sides of the transparent support, and in colors which are the same as the original object and complementary to the colors or the negative.

5. A process for producing, from a multi-color broken-tone picture of negative character, a multi-color photographic or cinematographic positive picture of highly transparent character, built up from two relief images of subtractive full-tone type formed of insolublized colored colloid containlng no silver, and in superimposed back to back registry, the said process comprising the following operations or steps:-(a) projecting two images both alike of the one multi-color broken-tone negativeJpicture on to opposite sides of a double- -sensitized positive nlm in superimposedrback-toback registry, the light-rays of the said negative images or broken-tone character being slightly spread diverted or scattered in the process of projection to form images of full-tone characaclaran ter; (o) separating the colors by a pair or complementary filters during projection, by exposing and printing one partial-positive image upon one side of the film. through a filter of one complementary color which cuts out all other colors but the one, and exposing and printing the other partial-positive image upon the other side of the film through a filter of the other complementary color which cuts out all other colors but the one; (c) developing and forming a pair of metallic silver images upon opposite sides of the iilni which are complemetary to each other; (d) a.p plying a layer oi colored colloid in liguid form to each of the metallic silver images, each laye; y

of colloid being of a color which is the same as the original subject and is complementary to the color of the negative, and is complementary to the other layer of colored colloid: (e) treating the colloid-colored film in a bleach-hardening bath to form images of insolubilized colored colloid; (f) dissolving the surplus colored colloid in a solvent bath; (g) dissolving the silver salts in another solvent bath; (h) finally Washing and.` drying the iilm; thereby producing a colorpositive comprising a. pair of colored-colloid relief images adhering toand superimposed upon a pair of silverless imageless transparent gelatine layers which are firmly adherent to opposite sides of the transparent support, and in colors which are the same as the original object and complementary to the colors of the negative,

JOHN EDWARD THORNTON. 

